Which browsers and operating systems support Let's Encrypt

This is a community-edited list of which operating systems / browsers can connect to servers that use Let’s Encrypt certificates. More specifically, these systems trust the IdenTrust “DST Root CA X3” certificate that cross-signs ISRG’s issuing certificates.

Android >= 2.3.6 (“DST Root CA X3” is included, see https://groups.google.com/a/letsencrypt.org/d/msg/client-dev/I-iFKihZ4Vo/kyw2EuaNlB0J, only tested >= 4.0 myself)



  • Internet Explorer (and other software which uses the Windows CryptoAPI) works (“DST Root CA X3” is included in Windows trust store; will be automatically downloaded if locally missing with Windows >= Vista; XP SP3 see below)
  • Google Chrome works (“DST Root CA X3” is included in Windows trust store; not on Windows XP, see below)
  • Pidgin >= 2.11 (“DST Root CA X3” is included, see https://developer.pidgin.im/ticket/16835)
  • Git for Windows >= 2.6 (“DST Root CA X3” is included)
  • Windows XP SP3 - Requires some extra work to support. Does not support SNI, and is also problematic regarding supported ciphers. Certificates issued prior to March 25 2016 were not trusted by Chrome, IE, and Safari on XP SP3. However, certificates issued after that date can work with XP SP3 if you manually configure ciphers.






Others known to work (based on https://groups.google.com/a/letsencrypt.org/d/msg/client-dev/I-iFKihZ4Vo/kyw2EuaNlB0J):

  • Amazon FireOS (Silk Browser)
  • Cyanogen 10,
  • Jolla Sailfish OS
  • Kindle v3.4.1


Known not to work (based on https://groups.google.com/a/letsencrypt.org/d/msg/client-dev/I-iFKihZ4Vo/kyw2EuaNlB0J)

  • Blackberry OS 6, 7 and 10.3.2 and below (>=10.3.3 should support Let’s Encrypt according to Inclusion of ISRG Root)
  • Android 2.3.5 (HTC Wildfire S, Stock Browser)
  • Nintendo 3DS
  • Windows XP-pre SP3 - cannot handle SHA256 signed certificates
  • Windows Live Mail (2012 mail client, not webmail) - according to Windows Live Mail revocation warning it is unable to handle certificates without a CRL.

trust chain is (in depth)

Your Server
Lets Encrypt X1 (must be sent as part of chain)
DST Root CA X3 (anchor)

for (almost) any other authority

Your Server
Intermediate (must be sent from server as part of chain)
CA Anchor (anchor, in browser storage)

so , as you can see there is no difference in certificate count in trust chain,
even there is no ISRG anchor at the moment, DST Root CA X3 acts like it.

And a worse example trust chain:

Your Server
Root CA (not trusted by some older clients, since CA bundles arent updated often) * cross signed
Other Root CA (anchor)

(WoSign has such chain, and other root ca is startcom)

LE is fine here, in the matter of being trusted by clients, propagating new anchor takes a lot of time

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If the Root CA is not in the browser no certificates based on that CA are trusted. And for older Android devices even the (established?) “DST Root CA X3” Root CA is not trusted… So, most CAs write “trusted by 99% of all devices” and list the browsers/OS where and when they got included. This would also be helpful for LE. - If your “users” mainly use older Android LE is not and will not be an option at all.

I already tried to make use of the intermediate certificate signed by the still hidden root … with mixed results. Root(s) missing, main cert chain not supported

Maybe someone can tell for what truststores and inclusion is requested?

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Terrific work, thank you very much for documenting this in such a clear and thorough way.


@jsha Hi would it be possible to track in an thread where letsencrypt have applyed for truststore inclusion like mozilla i mentioned under https://technet.microsoft.com/en-us/library/cc751157.aspx i found the link to http://aka.ms/rootcertapply and trustcert@microsoft.com and for applying. This information would maybe interesting for many people here too.

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Windows XP:

  • Pre-SP3 will never work, because it lacks SHA2 support.
  • SP3: Chrome and IE don’t currently work because of the name constraints on our intermediate. We’re going to take a look at whether that’s possible to work around in the long run, but for now it doesn’t work.
  • Firefox works because it has its own validation code.

also one more reason is down to server configuration of ssl cipher preferences, some folks may configure their servers with ssl ciphers that don't work with WinXP

Is there any place that collects information on whether LE is supported by various antivirus and MITM security vendors? I’ve encountered trouble with Avast. @mholt mentioned “multiple reports” about other Windows antivirus software in another thread

Would be useful to collect that info in addition to OS/browser support; we had to move off of letsencrypt for now because of trust issues with Avast.

This thread would be an appropriate place for such information. Can you provide additional details about the trouble you’ve had with Avast, including OS versions, browser versions, Avast product and version, and screenshots? Thanks!

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Thanks @jsha. I made a concerted effort to reproduce the problems with Avast myself in a VM but was unable to. After following up with the client, I found that they are on Windows XP SP3, and their syptoms are consistent with the known problems above: trust problems in IE and Chrome, but working in recent Firefox.

Long story short: I think our problem was not Avast, but the fact that the client was on Windows XP SP3. In all the iterations I tested, Avast was working fine in Win7, and disabling Avast on the client’s XP SP3 machine had (unsurprisingly) no effect.

So short of @mholt’s anecdotes in the other thread, I’ve got nothing to suggest there’s a problem with Avast, even when it’s configured to MITM HTTPS connections. Sorry for the FUD.

It's not entirely FUD. Granted, the certs used in that case were not from Let's Encrypt, but I am still wary of MITM in general, especially antivirus software.

I'd heartily agree to that, but happy that at least as far as it looks right now, LE doesn't appear to be "broken" by that dubious practice with Avast.

I exchanged messages with John Chen, the CEO of BlackBerry, today. BlackBerry’s security team is looking into adding support for Let’s Encrypt and recognizing the “DST Root CA X3” Root CA.

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I already created a thread there: https://community.letsencrypt.org/t/inclusion-of-isrg-root/.

https://helloworld.letsencrypt.org/ works in Fedora 22 and newer as well

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OS is Important if you use an Browser that does not have its own CA list.
Browser Version is Interesting with browsers having their own CA-List

that's why I use firefox. they not only have their own certs but also NSS meaning the MS'problems are not my problems. -> TLS 1.2, AES and EC even on XP (well I dont use it but you get my point.)